A circuit transfer function known as the Wilkinson power divider/combiner using distributed networks is shown in FIG. 1. It is a three port device having pods 4, 6, and 8. Impedance 10, of value Z.sub.o, may represent either a combining load or a source impedance. Transmission media 12 and 14 may be any sod of a transmission line such as, but not limited to, open wire line, coaxial cable, or wave guide. Each transmission medium 12 and 14 has a characteristic impedance equal to .sqroot.2 times Z.sub.o, as shown. The right end of each of these transmission media 12 and 14 is connected via impedance 16, of value 2 times Z.sub.o. Ports 6 and 8 are connected to impedances 22 and 24, each of impedance value Z.sub.o.
The divider/combiner of FIG. 1 may be considered as a divider if input port 4 is connected to a source of signal energy. As a divider, output ports 6 and 8 each produce one-half of the input power less the losses in the system. Impedance 10 represents the source impedance of the generator supplying the input power. Impedances 22 and 24 represent the load impedance of the two split loads. Each of the transmission media 12 and 14 are an odd multiple of one-quarter wavelength long at an operating frequency of interest in whatever media is provided.
If the network of FIG. 1 is used as a power combiner, impedances 22 and 24 represent the source impedances of two source power generators. Impedance 10 represents the impedance of the load.
The Wilkinson power divider/combiner of FIG. 1 is limited in that the input and output impedances are all equal to Z.sub.o. The design does not facilitate the use of different input and output impedances regardless of whether it is used as a combiner or a divider. Where input and output impedances are required to be different, prior art systems have typically accomplished the required matching by adding electrical transformer elements at input and/or output ports. These transformers may take the form of odd multiples of quarter wavelengths of transmission media having a characteristic impedance determined by the required input and output impedances which must be matched. This solution tends to provide a relatively expensive and bulky network. The larger networks reduce efficiency in terms of system losses.
These shortcomings were overcome by Dydyk as disclosed in U.S. Pat. No. 4,367,445, entitled "Impedance Transforming Three-Pod Power Divider" herein incorporated by reference and illustrated in FIG. 2. FIG. 2 is a more generalized version of FIG. 1, where the terminating impedances 32 and 34 at ports 6 and 8 are different from the generator impedance 30 at port 4. The Wilkinson power divider/combiner of FIG. 1 was modified in FIG. 2 to perform combining/dividing and impedance transformation using distributed networks with single and double sections of the Wilkinson concept.
There is a need of the same combining/dividing and impedance transformation functions in microwave monolithic integrated circuits (MMICs). To be cost effective, these functions must be accomplished without requiring a great deal of surface area on semiconductor die. Thus, using distributed networks at low microwave frequencies is not desirable.